Significant interaction occurs at the interface between dialysis membranes and blood during every hemodialysis procedure. This interaction results in marked neutropenia, hypoxemia and complement activation. Until recently, only cellulosic-type dialyzer membranes were available. Studies on how new types of membranes, polyacrylonitrile and poly (methyl methacrylate) have suggested that marked differences exist between these membranes and cellulosic membranes in the degree of neutropenia, hypoxemia and complement activation. The objective of this proposal is to compare the differences in the biocompatibility of these three dialysis membranes, in terms of their effect on red blood cells, neutrophils and lymphocytes, as well as complement activation and kinin generation. The effect of reusing these membranes on the nature and extent of these interactions will also be studied. In addition, a prospective study of renal failure patients prior to and after initiation of chronic hemodialysis with each of these three membranes will be included.